Solid-state imaging device having a switchable conversion gain in the floating diffusion, method for driving solid-state imaging device, and electronic apparatus

ABSTRACT

A solid-state imaging device and a method therefore capable of suppressing occurrence of motion distortion are provided. Each pixel includes a photo diode PD which accumulates a charge generated by photo-electric conversion in an accumulation period, a transfer transistor capable of transferring the accumulated charge in a transfer period, a floating diffusion FD to which the charge accumulated in the photo diode PD is transferred, a source-follower transistor which converts the charge of the floating diffusion FD to a voltage signal in accordance with the charge quantity, and a capacity changing portion capable of changing the capacity of the floating diffusion FD in accordance with a capacity changing signal, the capacity of the floating diffusion FD being changed by the capacity changing portion in a predetermined period in one readout period with respect to the accumulation period and a conversion gain being switched in this one readout period.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.15/154,229, filed on May 13, 2016, which contains subject matter relatedto Japanese Patent Application No. 2015-98806 filed in the Japan PatentOffice on May 14, 2015, the entire contents of which being incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a solid-state imaging device, a methodfor driving the solid-state imaging device, and an electronic apparatus.

BACKGROUND ART

As a solid-state imaging device (image sensor) using a photo-electricconversion element detecting light and generating a charge, a CMOS(Complementary Metal Oxide Semiconductor) image sensor has been put intopractical use. CMOS image sensors have been widely applied as parts ofdigital cameras, video cameras, monitoring cameras, medical endoscopes,personal computers (PC), mobile phones and another portable terminals(mobile devices), and various other electronic apparatuses.

A CMOS image sensor has photodiodes (photo-electric conversion elements)and floating diffusion (FD) amplifiers having FD layers corresponding tothe individual pixels. Readout is performed mainly by the columnparallel output method of selecting one row of the pixel array andsimultaneously reading out the pixels in the column output direction.

In this regard, in order to improve the characteristics, various methodsfor realizing a CMOS image sensor having a high image quality with awide dynamic range have been proposed (see for example PLT 1).

PLT 1 discloses a dynamic range widening technique for dividing theimaging into two or more exposure times different from each other, thatis, imaging corresponding to a high illuminance side by a short exposuretime and imaging corresponding to a low illuminance by a long exposuretime. Further, PLT 1 discloses a dynamic range widening technique whichmakes the capacities of the floating diffusions FD variable.

CITATION LIST Patent Literature

PLT 1. Japanese Patent Publication No. 2000-165754A

Technical Problem

However, in the dynamic range widening technique disclosed in PLT 1, theimaging by a low illuminance and the imaging by a high illuminance arecarried out at different times (periods), therefore signals obtained byplurality of exposures are used. Accordingly, there are thedisadvantages that the deviation occurs in the images, motion distortionoccurs, and the quality of a moving image is degraded.

SUMMARY OF INVENTION

The present invention provides a solid-state imaging device, a methodfor driving the solid-state imaging device, and an electronic apparatuscapable of suppressing occurrence of motion distortion while realizingwidening of dynamic range and in turn realizing a higher image quality.

A solid-state imaging device of a first aspect of the present inventionhas a pixel portion in which pixels are arranged, wherein each pixelincludes a photo-electric conversion element which accumulates a chargegenerated by photo-electric conversion in an accumulation period, atransfer element capable of transferring the charge accumulated in thephoto-electric conversion element in a transfer period, a floatingdiffusion to which the charge accumulated in the photo-electricconversion element is transferred through the transfer element, asource-follower element which converts the charge of the floatingdiffusion to a voltage signal in accordance with the charge quantity,and a capacity changing portion capable of changing the capacity of thefloating diffusion in accordance with a capacity changing signal, thecapacity of the floating diffusion being changed by the capacitychanging portion in a predetermined period in one readout period withrespect to the accumulation period and a conversion gain being switchedin this one readout period.

A second aspect of the present invention is a method for driving asolid-state imaging device having a pixel portion in which pixels arearranged, wherein each pixel includes a photo-electric conversionelement which accumulates a charge generated by photo-electricconversion in an accumulation period, a transfer element capable oftransferring the charge accumulated in the photo-electric conversionelement in a transfer period, a floating diffusion to which the chargesaccumulated in the photo-electric conversion element is transferredthrough the transfer element, a source-follower element which convertsthe charge of the floating diffusion to a voltage signal in accordancewith the charge quantity, and a capacity changing portion capable ofchanging the capacity of the floating diffusion in accordance with acapacity changing signal, comprising changing the capacity of thefloating diffusion by the capacity changing portion in the predeterminedperiod in one readout period with respect to the accumulation period andswitching a conversion gain in this one readout period.

An electronic apparatus of a third aspect of the present invention has asolid-state imaging device having a pixel portion in which pixels arearranged and an optical system for forming an object image at thesolid-state imaging device, wherein each pixel of the solid-stateimaging device includes a photo-electric conversion element whichaccumulates a charge generated by photo-electric conversion in anaccumulation period, a transfer element capable of transferring thecharge accumulated in the photo-electric conversion element in atransfer period, a floating diffusion to which the charge accumulated inthe photo-electric conversion element is transferred through thetransfer element, a source-follower element which converts the charge ofthe floating diffusion to a voltage signal in accordance with the chargequantity, and a capacity changing portion capable of changing thecapacity of the floating diffusion in accordance with a capacitychanging signal, the capacity of the floating diffusion being changed bythe capacity changing portion in a predetermined period in one readoutperiod with respect to the accumulation period and a conversion gainbeing switched in this one readout period.

Alternatively, a solid-state imaging device of another aspect of thepresent invention has the readout portion. The readout portion, duringthe readout scan period, sets a plurality of transfer periods forperforming transfer processing and performs the processing of readingout the signal in accordance with the accumulated charge in each readoutperiod after each transfer period.

Advantageous Effects of Invention

According to the present invention, it is possible to suppressoccurrence of motion distortion while realizing widening of the dynamicrange and in turn realize a higher image quality.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an example of the configuration of asolid-state imaging device according to a first embodiment of thepresent invention.

FIG. 2 is a circuit diagram showing an example of a pixel according tothe first embodiment.

FIG. 3A and FIG. 3B are diagrams showing operation timings of a shutterscan and readout scan at the time of usual readout operation in thepresent embodiment.

FIG. 4A to FIG. 4C are diagrams for explaining examples of theconfiguration of a readout system of column output of a pixel portion inthe solid-state imaging device according to the embodiment of thepresent invention.

FIG. 5A and FIG. 5B are diagrams showing a first example ofconfiguration of a MOS structure capacitor configuring a pixel and acapacity changing portion according to the first embodiment of thepresent invention.

FIG. 6A and FIG. 6B are diagrams showing a second example of theconfiguration of a MOS structure capacitor configuring a pixel and acapacity changing portion according to the first embodiment of thepresent invention.

FIG. 7A to FIG. 7C are diagrams for explaining the operation forrealizing a wide dynamic range in a case where the MOS structurecapacitor configuring the capacity changing portion according to thefirst embodiment is applied.

FIG. 8 is a diagram showing an example of the configuration of a pixeland capacity changing portion according to a second embodiment of thepresent invention.

FIG. 9A to FIG. 9D are diagrams for explaining the operation forrealizing a wide dynamic range in a case where a capacitor and a switchare applied to the capacity changing portion according to the secondembodiment.

FIG. 10 is a diagram showing an example of the configuration of a pixelportion and capacity changing portion according to a third embodiment ofthe present invention.

FIG. 11 is a timing chart for explaining the operation for realizing awide dynamic range in a case where a binning switch is applied to thecapacity changing portion according to the third embodiment.

FIG. 12 is a diagram showing an example of the configuration of a pixelportion and capacity changing portion according to a fourth embodimentof the present invention.

FIG. 13 is a timing chart for explaining the operation for realizing awide dynamic range in the case where the binning switch is applied tothe capacity changing portion according to the fourth embodiment.

FIG. 14 is a diagram showing an example of the configuration of a pixelportion and capacity changing portion according to a fifth embodiment ofthe present invention.

FIG. 15 is a timing chart of the operation for realizing a wide dynamicrange in a case where a binning switch is applied to the capacitychanging portion according to the fifth embodiment.

FIG. 16 is a diagram showing an example of the configuration of a pixelportion and capacity changing portion according to a sixth embodiment ofthe present invention.

FIG. 17 is a timing chart of the operation for realizing a wide dynamicrange in the case where the binning switch is applied to the capacitychanging portion according to the sixth embodiment.

FIG. 18 is a diagram for explaining that a solid-state imaging deviceaccording to the embodiment of the present invention can be applied toalso a shared pixel structure.

FIG. 19A and FIG. 19B are diagrams for explaining that the solid-stateimaging device according to the embodiment of the present invention canbe applied to both of a front-surface irradiation type image sensor anda back-surface irradiation type image sensor.

FIG. 20 is a diagram showing an example of the configuration of anelectronic apparatus to which a solid-state imaging device according toan embodiment of the present invention is applied.

DESCRIPTION OF EMBODIMENTS

Below, embodiments of the present invention will be explained withreference to the drawings.

First Embodiment

FIG. 1 is a block diagram showing an example of the configuration of asolid-state imaging device according to a first embodiment of thepresent invention. In the present embodiment, a solid-state imagingdevice 10 is configured by for example a CMOS image sensor.

This solid-state imaging device 10, as shown in FIG. 1, has a pixelportion 20 as an imaging portion, a vertical scanning circuit (rowscanning circuit) 30, a readout circuit (column readout circuit) 40, ahorizontal scanning circuit (column scanning circuit) 50, and a timingcontrol circuit 60 as principal components. Among these components, forexample, the vertical scanning circuit 30, readout circuit 40, andtiming control circuit 60 are used to configure a readout portion 70 ofa pixel signal.

In the present embodiment, in the solid-state imaging device 10, as willbe explained in detail later, the pixels which are arranged in the pixelportion 20 in a matrix state (or the pixel portion 20) are configured sothat each includes a capacity changing portion capable of changing thecapacity of a floating diffusion in accordance with a capacity changingsignal. In the solid-state imaging device 10, the capacity of a floatingdiffusion is changed by the capacity changing portion during oneaccumulation period of a charge (exposure period) or in a predeterminedperiod in one readout period after the accumulation period and aconversion gain is switched within this readout period.

In the present embodiment, the readout portion 70 is configured so thatit can perform, in one readout period, a first conversion gain modereading operation for reading out a pixel signal by a first conversiongain in accordance with a first capacity set by the capacity changingportion and a second conversion gain mode reading operation for readingout a pixel signal by a second conversion gain in accordance with asecond capacity (different from the first capacity) set by the capacitychanging portion. That is, the solid-state imaging device 10 of thepresent embodiment is provided as a solid-state imaging element having awide dynamic range, which outputs, with respect to the charge(electrons) which is generated by photo-electric conversion in oneaccumulation period (exposure period), a signal by switching the firstconversion gain (for example high conversion gain) mode and the secondconversion gain (low conversion gain) mode inside the pixel in onereadout period, and outputs both of a bright signal and a dark signal.

The readout portion 70 in the present embodiment basically performs thefirst conversion gain mode reading operation and second conversion gainmode reading operation in the accumulation period following a resetperiod for discharging the charge of the photodiode and the floatingdiffusion. Further, in the present embodiment, the readout portion 70,in the readout period after at least one transfer period which startsafter the readout period following the reset period, performs at leastone of the first conversion gain mode reading operation or secondconversion gain mode reading operation. That is, there also exists acase where both of the first conversion gain mode reading operation andthe second conversion gain mode reading operation are carried out in thereadout period after the transfer period.

In the usual pixel readout operation, by driving by the readout portion70, a shutter scan is carried out, then a readout scan is carried out.However, the first conversion gain mode reading operation (HCG) andsecond conversion gain mode reading operation (LCG) are carried out inthe readout scan period.

Below, after explaining the configurations and functions of the portionsof the solid-state imaging device in brief, the configuration of thecapacity changing portion, the readout processing concerned with that,and so on will be explained in detail.

Configurations of Pixel Portion 20 and Pixel PXL

In the pixel portion 20, a plurality of pixels each including aphotodiode (photo-electric conversion element) and a pixel amplifier arearranged in a two-dimensional matrix comprised of N rows and M columns.

FIG. 2 is a circuit diagram showing an example of a pixel according tothe present embodiment.

This pixel PXL has for example a photo-electric conversion elementcomprised of a photodiode (PD). For this photodiode PD, provision ismade of a transfer element comprised of a transfer transistor TG-Tr, areset element comprised of a reset transistor RST-Tr, a source-followerelement comprised of a source-follower transistor SF-Tr, and a selectionelement comprised of a selection transistor SEL-Tr.

Further, the pixel PXL has a capacity changing portion 80 which isconnected to a floating diffusion FD and can change the capacity of thefloating diffusion FD in accordance with a capacity changing signal CS.

The photodiode PD generates a signal charge (electrons) of a quantity inaccordance with the incident light quantity and accumulates (stores) thesame. Below, an explanation will be given of a case where the signalcharge is comprised of electrons and each transistor is an n-typetransistor. However, the signal charge may be a hole or each transistormay be a p-type transistor as well. Further, the present embodiment iseffective even in a case where each transistor is shared among aplurality of photodiodes and a case where a three-transistor (3Tr) pixelnot having a selection transistor is employed.

The transfer transistor TG-Tr is connected between the photodiode PD andthe floating diffusion FD and is controlled through a control line TG.The transfer transistor TG-Tr is selected in a period where the controlline TG is at a high level H and becomes a conductive state andtransfers a charge (electrons) which is generated by photo-electricconversion and accumulated (stored) in the photodiode PD to the floatingdiffusion FD.

The reset transistor RST-Tr is connected between a power supply lineVRst and the floating diffusion FD and is controlled through a controlline RST. Note that, the reset transistor RST-Tr may be configured sothat it is connected between a power supply line VDD and the floatingdiffusion FD and is controlled through the control line RST as well. Thereset transistor RST-Tr is selected in the period where the control lineRST is at the H level and becomes a conductive state and resets thefloating diffusion FD to a potential of the power supply line VRst (orVDD).

The source-follower transistor SF-Tr and the selection transistor SEL-Trare connected in series between the power supply line VDD and a verticalsignal line LSGN. To a gate of the source-follower transistor SF-Tr, thefloating diffusion FD is connected. The selection transistor SEL-Tr iscontrolled through a control line SEL. The selection transistor SEL-Tris selected in the period where the control line SEL is at the H leveland becomes a conductive state. Due to this, the source-followertransistor SF-Tr outputs a readout signal VSL of column output obtainedby converting the charge of the floating diffusion FD to a voltagesignal in accordance with the charge quantity (potential) to thevertical signal line LSGN. These operations are for example carried outsimultaneously in parallel for each of one row's worth of the pixelssince gates of the transfer transistor TG-Tr, reset transistor RST-Tr,and the selection transistor SEL-Tr are connected in units of rows.

In the pixel portion 20, pixels PXL are arranged in N rows and Mcolumns, therefore the number of each of the control lines SEL, RST, andTG is N, and the number of the vertical signal lines LSGN is M. In FIG.1, each of the control lines SEL, RST, and TG is expressed as one rowscanning control line.

The vertical scanning circuit 30 drives pixels through the row scanningcontrol line in the shutter row and readout row in accordance with thecontrol of the timing control circuit 60. Further, the vertical scanningcircuit 30 outputs a row selection signal having a row address of a readrow for reading out the signal and a shutter row for resetting thecharge accumulated in the photodiode PD according to the address signal.

As explained above, in the usual pixel readout operation, by driving bythe vertical scanning circuit 30 of the readout portion 70, the shutterscan is carried out, then the readout scan is carried out.

FIG. 3A and FIG. 3B are diagrams showing operation timings of theshutter scan and the readout scan at the time of the usual pixel readoutoperation in the present embodiment. FIG. 3A shows the relationshipsamong the shutter scan, exposure period, and readout scan, and FIG. 3Bshows concrete operation timings of the shutter scan and readout scan.

The control line SEL which controls the ON (conductive) and OFF(nonconductive) states of the selection transistor SEL-Tr is set at an Llevel in the shutter scan period PSHT so that the selection transistorSEL-Tr is held in the nonconductive state, while is set at an H level inthe readout scan period PRDO so that the selection transistor SEL-Tr isheld in the conductive state. Further, in the shutter scan period PSHT,the control line TG is set at an H level in the predetermined period forthe period where the control line RST is at the H level, and thephotodiode PD and floating diffusion FD are reset through the resettransistor RST-Tr and transfer transistor TG-Tr.

In the readout scan period PRDO, the control line RST is set at the Hlevel, the floating diffusion FD is reset through the reset transistorRST-Tr, and the signal in the reset state is read out in a readoutperiod PRD1 after this reset period PR. After the readout period PRD1,for the predetermined period, the control line TG is set at an H level,the accumulated charge in the photodiode PD is transferred through thetransfer transistor TG-Tr to the floating diffusion FD, and a signal inaccordance with the accumulated electrons (charge) is read out in areadout period PRD2 after this transfer period PT.

Note that, in the usual pixel readout operation in the first embodiment,as shown in FIG. 3B, the accumulation period (exposure period) EXP isthe period from when the control line TG is switched to the L levelafter resetting the photodiode PD and floating diffusion FD during theshutter scan period PSHT to when the control line TG is switched to theL level in order to end the transfer period PT during the readout scanperiod PRDO.

The readout circuit 40 may be configured so that it includes a pluralityof column signal processing circuits (not shown) which are arrangedcorresponding to the column outputs of the pixel portion 20 and so thatcolumn parallel processing is possible in the plurality of column signalprocessing circuits.

The readout circuit 40 can be configured including a correlated doublesampling (CDS) circuit and ADC (analog/digital converter: AD converter),amplifier (AMP), sample/hold (S/H) circuit, and so on.

In this way, the readout circuit 40, for example as shown in FIG. 4A,may be configured by including an ADC 41 which converts a readout signalVSL of each column output of the pixel portion 20 to a digital signal.Otherwise, in the readout circuit 40, for example as shown in FIG. 4B,an amplifier (AMP) 42 for amplifying the readout signal VSL of eachcolumn output of the pixel portion 20 may be arranged. Further, in thereadout circuit 40, for example as shown in FIG. 4C, a sample/hold (S/H)circuit 43 for sampling and holding the readout signal VSL of eachcolumn output of the pixel portion 20 may be arranged.

The horizontal scanning circuit 50 scans the signals processed in theADC and other of the plurality of column signal processing circuits inthe readout circuit 40, transfers the results in the horizontaldirection, and outputs the same to a not shown signal processingcircuit.

The timing control circuit 60 generates the timing signals which arenecessary for the signal processing of the pixel portion 20, verticalscanning circuit 30, readout circuit 40, horizontal scanning circuit 50,and so on.

The configurations and functions of the different portions in thesolid-state imaging device 10 were explained in brief above. Next, theconfiguration of the capacity changing portion 80 according to the firstembodiment and the readout processing etc. related with this will beexplained in detail.

In the first embodiment, the capacity changing portion 80 is configuredby a MOS structure capacitor which is connected to the floatingdiffusion FD of each pixel PXL.

FIG. 5A and FIG. 5B are diagrams showing a first example of theconfiguration of the MOS structure capacitor which configures the pixeland capacity changing portion according to the first embodiment of thepresent invention. FIG. 5A shows an equivalent circuit of a pixel PXLincluding a MOS structure capacitor 81 of the first example of theconfiguration, and FIG. 5B simply shows the cross-sectional structure ofthe MOS structure capacitor 81 in the first example of theconfiguration.

In this MOS structure capacitor 81, a drain and a source of the MOS areconnected, the connecting point thereof is connected to the floatingdiffusion FD, and a gate is connected to the supply line of the capacitychanging signal CS. In the MOS structure capacitor 81, the drain 811 andthe source 812 are formed as for example n+ diffusion layers which arethe first conductivity type on the two end sides of a channel formingregion 813 of a semiconductor substrate. These n+ diffusion layers areconnected to each other and are connected to the floating diffusion FD.Further, in the MOS structure capacitor 81, the gate 814 is formed bypolysilicon through a gate oxide film 815 on the channel forming region813 of the semiconductor substrate. This gate 814 is connected to thesupply line of the capacity changing signal CS.

Note that, the MOS structure capacitor 81 may be configured as a buriedchannel as well so as to improve the linearity.

In this first embodiment, by making the MOS structure capacitor 81function as a variable capacitance by switching the gate voltage of theMOS structure capacitor 81 by the capacity changing signal CS, thedynamic range is extended. The processing of extending the dynamic rangeby making the MOS structure capacitor 81 function as a variablecapacitance by switching the gate voltage of the MOS structure capacitor81 by the capacity changing signal CS is carried out in the readout scanperiod PRDO which was explained with reference to FIG. 3A and FIG. 3B.As explained before, the control line SEL is set at the H level in thereadout scan period PRDO and the selection transistor SEL-Tr is held inthe conductive state.

When the capacity changing signal CS is at a low level L, the capacity(charge quantity) of the floating diffusion FD is not changed. In thiscase, during the readout scan period PRDO, for example, in one readoutperiod PRD1 from when the floating diffusion FD is reset through thereset element comprised of the reset transistor RST-Tr in the resetperiod PR up to when the transfer period PT is started, the readoutportion 70 performs a high conversion gain mode reading operation HCG1for reading out the pixel signal by a high conversion gain (firstconversion gain) in accordance with the first capacity (the firstcapacity may be a capacity which is not changed by a default value)which is set by the MOS structure capacitor 81 in the capacity changingportion 80. Alternatively, with the use of the readout portion 70, forexample, in one readout period PRD2 (PRD3) after the accumulated chargein the photodiode PD is transferred to the floating diffusion FD throughthe transfer element comprised of the transfer transistor TG-Tr in thetransfer period PT, the readout portion 70 performs a high conversiongain mode reading operation HCG2 for reading out the pixel signal by ahigh conversion gain (first conversion gain) in accordance with thefirst capacity set by the MOS structure capacitor 81 in the capacitychanging portion 80.

When the capacity changing signal CS is at the H (high level), thecapacity is changed so that the capacity (charge quantity) of thefloating diffusion FD increases. In this case, during the readout scanperiod PRDO, for example, in one readout period PRD1 from when thefloating diffusion FD is reset through the reset element comprised ofthe reset transistor RST-Tr in the reset period PR up to when thetransfer period PT is started, the readout portion 70 performs a lowconversion gain mode reading operation LCG1 for reading out the pixelsignal by a low conversion gain (second conversion gain) in accordancewith the second capacity (in accordance with the second capacity whichis changed from the default first capacity) which is set by the MOSstructure capacitor 81 in the capacity changing portion 80.Alternatively, with the use of the readout portion 70, for example, inone readout period PRD2 (PRD3) after the accumulated charge in thephotodiode PD is transferred to the floating diffusion FD through thetransfer element comprised of the transfer transistor TG-Tr in thetransfer period PT, the readout portion 70 performs a low conversiongain mode reading operation LCG2 for reading out the pixel signal by alow conversion gain (second conversion gain) in accordance with thesecond capacity set by the MOS structure capacitor 81 in the capacitychanging portion 80.

Further, for example, in the readout circuit 40 configuring a portion ofthe readout portion 70, a difference between the readout signal of thehigh conversion gain mode reading operation HCG2 and the readout signalof the high conversion gain mode reading operation HCG1 is taken, andCDS processing is carried out. In the same way, a difference between thereadout signal of the low conversion gain mode reading operation LCG2and the readout signal of the low conversion gain mode reading operationLCG1 is taken, and CDS processing is carried out.

In this way, the solid-state imaging device 10 in the first embodimentis realized as a solid-state imaging element having a wide dynamic rangein which, with respect to the charge (electrons) which is generated byphoto-electric conversion in one accumulation period (exposure period),inside the pixel, signals are output by switching the first conversiongain (for example high conversion gain) mode and the second conversiongain (low conversion gain) mode so both of a bright signal and the darksignal are output in one readout period.

FIG. 6A and FIG. 6B are diagrams showing a second example of theconfiguration of the MOS structure capacitor configuring a pixel andcapacity changing portion according to the first embodiment of thepresent invention. FIG. 6A shows an equivalent circuit of a pixel PXLincluding a MOS structure capacitor 81A of the second example of theconfiguration, and FIG. 6B simply shows the cross-sectional structure ofthe MOS structure capacitor 81A of the second example of theconfiguration.

The point of difference of this MOS structure capacitor 81A of thesecond example of the configuration from the MOS structure capacitor 81of the first example of the configuration which was explained above isas follows. In the MOS structure capacitor 81A of the second example ofthe configuration, only the region of the drain 811 of the n+ diffusionlayer is connected to the floating diffusion FD, and a source 812A isformed as a second conductivity type p+ diffusion layer region.

In this way, by injecting p-type ions into a diffusion layer which ispositioned at the distant side of the floating diffusion FD node, itbecomes possible to reduce the remaining charge under the gate at thetime of switching the gate voltage.

Next, the operation for realizing a wide dynamic range in a case wherethe MOS structure capacitor configuring the capacity changing portionaccording to the first embodiment is applied will be explained withreference to FIG. 7A to FIG. 7C.

FIG. 7A to FIG. 7C are diagrams for explaining the operation forrealizing a wide dynamic range in a case where the MOS structurecapacitor configuring the capacity changing portion according to thefirst embodiment is applied. FIG. 7A shows an example of a case wherethe MOS structure capacitor 81A of the second example of theconfiguration in FIG. 6B is applied as the MOS structure capacitorconfiguring the capacity changing portion. FIG. 7A shows an equivalentcircuit of the pixel PXL, FIG. 7B shows a timing chart for explainingthe operation, and FIG. 7C diagrammatically shows a transition of thepotential of a principal part of the pixel PXL along with the elapse oftime of operation.

Note that, in the present embodiment, the explanation will be given byassuming that between the first capacity and second capacity which areset by the capacity changing portion 80, the second capacity is largerthan the first capacity. These values are relative ones. Forfacilitating understanding, they will be explained as the first capacityand second capacity also in the two periods which are after the resetperiod and after the transfer period.

During the readout scan period PRDO, as shown in FIG. 7B, in order toselect one row in the pixel array, the control line SEL connected toeach pixel PXL in that selected row is set at the H level and theselection transistor SEL-Tr of the pixel PXL becomes a conductive state.In this selection state, the reset transistor RST-Tr is selected in thereset period PR in the period where the control line RST is at the Hlevel to become a conductive state, and the floating diffusion FD isreset to the potential of the power supply line VDD. The period fromwhen this reset period PR passes (the reset transistor RST-Tr is in anonconductive state) up to when the transfer period PT is startedbecomes the first readout period PRD1 for reading out the pixel signalat the time of the reset state.

At a time t1 after the first readout period PRD1 is started, thecapacity changing signal CS is set at the L level, and the readoutportion 70 performs the first high conversion gain mode readingoperation HCG1 for reading out the pixel signal by a high conversiongain (first conversion gain) so that the capacity (charge quantity) ofthe floating diffusion FD is not changed from the first capacity. Atthis time, in each pixel PXL, due to the source-follower transistorSF-Tr, the charge in the floating diffusion FD is converted to a voltagesignal in accordance with the charge quantity (potential). This isoutput as the readout signal VSL (HCG1) of column output to the verticalsignal line LSGN, supplied to the readout circuit 40, and for exampleheld.

In the first readout period PRD1, after the first high conversion gainmode reading operation HCG1 is carried out at the time t1, the capacitychanging signal CS is switched to the H level and the capacity ischanged so that the capacity (charge quantity) of the floating diffusionFD increases from the first capacity to the second capacity. Further, ata time t2, the readout portion 70 performs a first low conversion gainmode reading operation LCG1 for reading out the pixel signal by a lowconversion gain (second conversion gain) by the change of the capacity(charge quantity) of the floating diffusion FD. At this time, in eachpixel PXL, due to the source-follower transistor SF-Tr, the charge inthe floating diffusion FD is converted to the voltage signal inaccordance with the charge quantity (potential). This is output as thereadout signal VSL (LCG1) of column output to the vertical signal lineLSGN, supplied to the readout circuit 40, and for example held.

Here, the first readout period PRD1 ends, and the transfer period PTstarts. Note that, at this time, the capacity changing signal CS is heldat the H level as it is in a predetermined period after the transferperiod PT passes. In the transfer period PT, the transfer transistorTG-Tr is selected in the period where the control line TG is at the highlevel H and becomes a conductive state, and the charge (electrons) whichis generated by photo-electric conversion and accumulated in thephotodiode PD is transferred to the floating diffusion FD. After thistransfer period PT passes (the transfer transistor TG-Tr is in thenonconductive state), the second readout period PRD2 for reading out thepixel signal in accordance with the charge which is generated byphoto-electric conversion and accumulated in the photodiode PD starts.

At a time t3 after the second readout period PRD2 is started, in thestate where the capacity changing signal CS is set at the H level, thereadout portion 70 performs a second low conversion gain mode readingoperation LCG2 for reading out the pixel signal by a low conversion gain(second conversion gain) by the change of the capacity (charge quantity)of the floating diffusion FD. At this time, in each pixel PXL, due tothe source-follower transistor SF-Tr, the charge in the floatingdiffusion FD is converted to a voltage signal in accordance with thecharge quantity (potential). This is output as the readout signal VSL(LCG2) of column output to the vertical signal line LSGN, supplied tothe readout circuit 40, and for example held.

In the second readout period PRD2, after the second low conversion gainmode reading operation LCG2 is carried out at the time t3, the capacitychanging signal CS is switched to the L level to change the capacity sothat the capacity (charge quantity) of the floating diffusion FD isreduced from the second capacity to the first capacity. Further, at atime t4, the readout portion 70 performs a second high conversion gainmode reading operation HCG2 for reading out the pixel signal by a highconversion gain (first conversion gain) by the change so that thecapacity (charge quantity) of the floating diffusion FD becomes low. Atthis time, in each pixel PXL, due to the source-follower transistorSF-Tr, the charge in the floating diffusion FD is converted to a voltagesignal in accordance with the charge quantity (potential). This isoutput as the readout signal VSL (HCG2) of column output to the verticalsignal line LSGN, supplied to the readout circuit 40, and for exampleheld.

Further, in for example the readout circuit 40 configuring a portion ofthe readout portion 70, a difference {VSL(HCG2)−VSL(HCG1)} between thereadout signal VSL (HCG2) of the second high conversion gain modereading operation HCG2 and the readout signal VSL (HCG1) of the firsthigh conversion gain mode reading operation HCG1 is taken, and CDSprocessing is carried out. In the same way, in the readout circuit 40, adifference {VSL(LCG2)−VSL(LCG1)} between the readout signal VSL (LCG2)of the second low conversion gain mode reading operation LCG2 and thereadout signal VSL (LCG1) of the first low conversion gain mode readingoperation LCG1 is taken, and CDS processing is carried out.

In this way, the solid-state imaging device 10 in the first embodimentrealizes a wide dynamic range of outputting signals by switching thehigh conversion gain (first conversion gain) mode and the low conversiongain (second conversion gain) mode and outputting both of a brightsignal and a dark signal in one readout period inside the pixel withrespect to the charge (electrons) which is generated by photo-electricconversion in one accumulation period (exposure period).

As explained above, according to the first embodiment, the capacity ofthe floating diffusion FD is changed by the capacity changing portion 80(80A) configured by the MOS structure capacitor 81 (81A) in apredetermined period in one readout period of charge, and the conversiongain is switched in this readout period. Further, the readout portion70, in one readout period, performs the high conversion gain (firstconversion gain) mode reading operation for reading out the pixel signalby high conversion gain (first conversion gain) in accordance with thefirst capacity which is set by the capacity changing portion 80 (80A),and the low conversion gain (second conversion gain) mode readingoperation for reading out the pixel signal by the low conversion gain(second conversion gain) in accordance with the second capacity which isset by the capacity changing portion 80 (80A).

Accordingly, according to the first embodiment, with respect to thecharge (electrons) which is generated by photo-electric conversion inone accumulation period (exposure period), inside the pixel, signals areoutput by switching the high conversion gain mode and the low conversiongain mode so both of a bright signal and dark signal can be output inone readout period, a reset noise at the time of high conversion gainmode and low conversion gain mode can be cancelled, a dynamic rangewidening can be realized while suppressing occurrence of motiondistortion, and consequently a higher image quality can be realized.

Second Embodiment

FIG. 8 is a diagram showing an example of the configuration of a pixeland a capacity changing portion according to a second embodiment of thepresent invention.

The difference of a capacity changing portion 80B in the secondembodiment from the capacity changing portion 80 in the first embodimentresides in that, in place of the configuration by the MOS structurecapacitor, it is configured by a capacitor 82 and a switch comprised ofa switching transistor 83 which is connected between the capacitor 82and the floating diffusion FD and is turned ON or OFF in accordance withthe capacity changing signal CSG.

Next, the operation for realizing a wide dynamic range in a case wherethe capacitor and switch are applied to the capacity changing portionaccording to the second embodiment will be explained with reference toFIG. 9A to FIG. 9D.

FIG. 9A to FIG. 9D are diagrams for explaining the operation forrealizing a wide dynamic range in a case where the capacitor and switchare applied to the capacity changing portion according to the secondembodiment. FIG. 9A shows an equivalent circuit of the pixel PXL, FIG.9B shows a timing chart for explaining the operation, FIG. 9Cdiagrammatically shows the transition of the potential of the principalpart of the pixel PXL along with the elapse of time of the operation,and FIG. 9D shows the relationship between the illuminance and the CDSoutput.

During the readout scan period PRDO, as shown in FIG. 9B, in order toselect one row in the pixel array, the control line SEL connected toeach pixel PXL in that selected row is set at an H level and theselection transistor SEL-Tr of the pixel PXL becomes a conductive state.In this selection state, the reset transistor RST-Tr is selected in thereset period PR in the period where the control line RST is at the Hlevel to become a conductive state, and the floating diffusion FD isreset to the potential of the power supply line VDD. The period afterthis reset period PR passes (the reset transistor RST-Tr is in anonconductive state) and up to when the transfer period PT is startedbecomes a first readout period PRD11 for reading out the pixel signal atthe time of the reset state. Substantially parallel to the start of thereset period PR, the capacity changing signal CSG is switched to the Hlevel, and the capacity is changed so that the capacity (chargequantity) of the floating diffusion FD increases from the first capacityto the second capacity.

At the time t1 after the first readout period PRD11 is started, in thestate where the capacity changing signal CSG is held at the H level, thereadout portion 70 performs a first low conversion gain mode readingoperation LCG11 for reading out the pixel signal by a low conversiongain (second conversion gain) by the change of the capacity (chargequantity) of the floating diffusion FD to the second capacity. At thistime, in each pixel PXL, due to the source-follower transistor SF-Tr,the charge in the floating diffusion FD is converted to a voltage signalin accordance with the charge quantity (potential). This is output asthe readout signal VSL (LCG11) of column output to the vertical signalline LSGN, supplied to the readout circuit 40, and for example held.

In the first readout period PRD11, after the first low conversion gainmode reading operation LCG11 is carried out at the time t1, the capacitychanging signal CSG is switched to the L level, and the capacity ischanged so that the capacity (charge quantity) of the floating diffusionFD is reduced from the second capacity to the first capacity. Further,at the time t2, the readout portion 70 performs a first high conversiongain mode reading operation HCG11 for reading out the pixel signal by ahigh conversion gain (first conversion gain) by the change of thecapacity (charge quantity) of the floating diffusion FD. At this time,in each pixel PXL, due to the source-follower transistor SF-Tr, thecharge in the floating diffusion FD is converted to a voltage signal inaccordance with the charge quantity (potential). This is output as thereadout signal VSL (HCG11) of column output to the vertical signal lineLSGN, supplied to the readout circuit 40, and for example held.

Here, the first readout period PRD11 ends, and the first transfer periodPT11 starts. Note that, at this time, the capacity changing signal CSGis held at the L level as it is in a predetermined period after thefirst transfer period PT11 passes to substantially the time immediatelybefore the start of the next second transfer period PT12. In the firsttransfer period PT11, the transfer transistor TG-Tr is selected tobecome a conductive state in the period where the control line TG is atthe H level, and the charge (electrons) which is generated byphoto-electric conversion and accumulated in the photodiode PD istransferred to the floating diffusion FD. After this first transferperiod PT passes (the transfer transistor TG-Tr is in a nonconductivestate), the second readout period PRD12 for reading out the pixel signalin accordance with the charge which is generated by photo-electricconversion and accumulated in the photodiode PD starts.

At the time t3 after the second readout period PRD12 is started, in thestate where the capacity changing signal CSG is set at the L level, thereadout portion 70 performs the second high conversion gain mode readingoperation HCG12 for reading out the pixel signal by a high conversiongain (first conversion gain) in the case where the capacity (chargequantity) of the floating diffusion FD is set at the first capacity. Atthis time, in each pixel PXL, due to the source-follower transistorSF-Tr, the charge in the floating diffusion FD is converted to a voltagesignal in accordance with the charge quantity (potential). This isoutput as the readout signal VSL (HCG12) of column output to thevertical signal line LSGN, supplied to the readout circuit 40, and forexample held.

In the second readout period PRD12, after the second high conversiongain mode reading operation HCG12 is carried out at the time t3, thecapacity changing signal CSG is switched to the H level, and thecapacity is changed so that the capacity (charge quantity) of thefloating diffusion FD increases from the first capacity to the secondcapacity. Substantially parallel to this capacity change, the secondtransfer period PT12 starts. Note that, at this time, the capacitychanging signal CSG is held at the H level as it is after the secondtransfer period PT12 passes up to when the control line SEL is switchedto the L level. In the second transfer period PT12, the transfertransistor TG-Tr is selected and becomes a conductive state for theperiod where the control line TG is at the H level, and the charge(electrons) which is generated by photo-electric conversion andaccumulated in the photodiode PD is transferred to the floatingdiffusion FD. After this second transfer period PT12 passes (thetransfer transistor TG-Tr is in a nonconductive state), a third readoutperiod PRD13 for further reading out the pixel signal in accordance withthe charge which is generated by photo-electric conversion andaccumulated in the photodiode PD starts.

At a time t4 after the third readout period PRD13 is started, in thestate where the capacity changing signal CSG is held at the H level, thereadout portion 70 performs the second low conversion gain mode readingoperation LCG12 for reading out the pixel signal by a low conversiongain (second conversion gain) in the case where the capacity (chargequantity) of the floating diffusion FD is set at the second capacity. Atthis time, in each pixel PXL, due to the source-follower transistorSF-Tr, the charge in the floating diffusion FD is converted to a voltagesignal in accordance with the charge quantity (potential). This isoutput as the readout signal VSL (LCG12) of column output to thevertical signal line LSGN, supplied to the readout circuit 40, and forexample held.

Further, for example, in the readout circuit 40 configuring a portion ofthe readout portion 70, a difference {VSL(HCG12)−VSL(HCG11)} between thereadout signal VSL (HCG12) of the second high conversion gain modereading operation HCG12 and the readout signal VSL (HCG11) of the firsthigh conversion gain mode reading operation HCG11 is taken, and CDSprocessing is carried out. In the same way, in the readout circuit 40, adifference {VSL(LCG12)−VSL(LCG11)} between the readout signal VSL(LCG12) of the second low conversion gain mode reading operation LCG12and the readout signal VSL (LCG11) of the first low conversion gain modereading operation LCG11 is taken, and CDS processing is carried out.

According to the second embodiment, the same effects as those by thefirst embodiment explained above can be obtained. That is, according tothe second embodiment, the following effects can be obtained: Withrespect to the charge (electrons) which is generated by photo-electricconversion in one accumulation period (exposure period), inside thepixel, in one readout period, signals are output by switching the highconversion gain mode and the low conversion gain mode so both of thebright signal and dark signal can be output, a reset noise at the timeof high conversion gain mode and low conversion gain mode can becancelled, dynamic range widening can be realized while suppressingoccurrence of motion distortion, and consequently a higher image qualitycan be realized.

Further, according to the second embodiment, the readout portion 70,during the readout scan period PRDO, sets a plurality of (two in thepresent example) transfer periods for performing transfer processing andperforms the processing of reading out the signal in accordance with theaccumulated charge in each readout period after each transfer period,therefore it becomes possible to reliably realize a further widening ofdynamic range. Further, according to the second embodiment, the readoutportion 70, in at least one transfer period (the transfer period on thelatter stage side in the present example) among the plurality oftransfer periods, transfers the accumulated charge from thephoto-electric conversion element PD in a state where the capacity ofthe floating diffusion is made large by the capacity changing portion,therefore it becomes possible to reduce an overflowing charge, theaccumulated charge can be effectively utilized, and consequently ahigher image quality can be realized.

Third Embodiment

FIG. 10 is a diagram showing an example of the configuration of a pixelportion and capacity changing portion according to a third embodiment ofthe present invention.

The difference of a capacity changing portion 80C in the thirdembodiment from the capacity changing portion 80 in the first and secondembodiments is as follows. In the first and second embodiments, thecapacity changing portion is configured by the MOS structure capacitor,switch, and capacitor.

Contrary to this, in the third embodiment, the capacity changing portion80C is configured by not a capacitor, but a first binning switch 84 _(n)which is connected to (arranged in) wiring WR formed between thefloating diffusions FD of two pixels PXL_(n) and PXL_(n+1) which areadjacent in the column output direction and a first binning switch 84_(n+1) which is connected between the floating diffusion FD of the pixelPXL_(n+1) and the power supply line VDD. In the third embodiment, byturning on/off the first binning switches 84 _(n) and 84 _(n+1) bycapacity changing signals BIN_(n) and BIN_(n+1), the number of thefloating diffusions FD to be connected is switched to one or two or more(two in the present example) to thereby change the capacity of thefloating diffusion FD of the readout target pixel and switch theconversion gain of the floating diffusion FD of the pixel PXL_(n) orPXL_(n+1) to be read out.

In other words, in the third embodiment, the reset element is shared bythe two adjacent pixels PXL_(n) and PXL_(n+1) in one column, thefloating diffusion FD of the pixel PXL_(n) and the power supply line VDDare connected to each other through the first binning switches 84 _(n)and 84 _(n+1) which are formed so as to be cascade connected to thewiring WR, and a connection node ND_(n+1) on the wiring WR between thefirst binning switches 84 _(n) and 84 _(n+1) and the floating diffusionFD of the pixel PXL_(n+1) are connected. In the third embodiment, thefirst binning switch 84 _(n+1) functions as the shared reset element.

In the present embodiment, the first binning switch 84 ( . . . , n−1, n,n+1, . . . ) is for example formed by an n-channel MOS (NMOS)transistor. In the following explanation, the binning switch will besometimes called a “binning transistor” as well.

By providing the first binning switches 84 _(n) and 84 _(n+1) in thisway, the capacitor and reset transistor become unnecessary for thepixels PXL_(n) and PXL_(n+1), the number of transistors in a pixel canbe decreased, an aperture ratio of the photodiode PD is high, and thephoto-electric conversion sensitivity and number of saturated electronscan be raised. In the third embodiment, the first binning switches 84_(n) and 84 _(n+1) have the function as a reset element together.Further, all of plurality of (two in the present example) pixelsconnected through the first binning switches 84 _(n) and 84 _(n+1) sharethe reset element by the first binning switch 84 _(n+1) which dischargesthe charge in the floating diffusion FD in the reset period PR.

In the third embodiment, by making the capacity changing signalBIN_(n+1) corresponding to the readout pixel PXL_(n+1) an L level, thisis rendered a non-reset state.

In this way, in the third embodiment, pixels are provided where twopixels of one column share a reset element. Therefore, at the time ofresetting the floating diffusion FD, a resistance between the floatingdiffusion FD and the reset electrode is low, so an excellent speed isachieved in the reset operation.

Next, an operation for realizing a wide dynamic range where a binningswitch (binning transistor) is applied to the capacity changing portionaccording to the third embodiment will be explained with reference toFIG. 11.

FIG. 11 is a timing chart for explaining the operation for realizing awide dynamic range where a binning switch (binning transistor) isapplied to the capacity changing portion according to the thirdembodiment.

During the readout scan period PRDO, as shown in FIG. 11, in order toselect one row in the pixel array, for example, the n-th row, thecontrol line SEL connected to each pixel PXL_(n) in that selected row isset at the H level and the selection transistor SEL-Tr in the pixelPXL_(n) becomes a conductive state. In this selection state, in thereset period PR21, all first binning transistors 84 _(n), 84 _(n+1) (84_(n−1) . . . ) are selected and become a conductive state in a periodwhere the capacity changing signals BIN_(n) and BIN_(n+1) are at the Hlevel as the reset signals, and the floating diffusions FD are reset tothe potential of the power supply line VDD. After this reset period PR21passes, the capacity changing signal BIN_(n+1) is switched to the Llevel and the first binning transistor 84 _(n+1) is switched to anonconductive state. On the other hand, the capacity changing signalBIN_(n) is held at the H level as it is, and the first binningtransistor 84 _(n) is held in the conductive state. The reset periodPR21 ends by the first binning transistor 84 _(n+1) being switched tothe nonconductive state and the first binning transistor 84 _(n) beingheld in the conductive state, and the capacity (charge quantity) of thefloating diffusion FD of the pixel PXL_(n) is changed so as to increasefrom the first capacity to the second capacity. Further, the period upto the start of the transfer period PT21 becomes the first readoutperiod PRD21 for reading out the pixel signal at the time of the resetstate.

At the time t1 after the first readout period PRD21 is started, in thestate where the capacity changing signal BIN_(n) is held at the H level,the readout portion 70 performs a first low conversion gain mode readingoperation LCG21 for reading out the pixel signal by a low conversiongain (second conversion gain) by the change of the capacity (chargequantity) of the floating diffusion FD to the second capacity. At thistime, in each pixel PXL_(n), due to the source-follower transistorSF-Tr, the charge in the floating diffusion FD is converted to a voltagesignal in accordance with the charge quantity (potential). This isoutput as the readout signal VSL (LCG21) of column output to thevertical signal line LSGN, supplied to the readout circuit 40, and forexample held.

In the first readout period PRD21, after the first low conversion gainmode reading operation LCG21 is carried out at the time t1, the capacitychanging signal BIN_(n) is switched to the L level, and the capacity(charge quantity) of the floating diffusion FD is changed so as todecrease from the second capacity to the first capacity. Further, at thetime t2, the readout portion 70 performs a first high conversion gainmode reading operation HCG21 for reading out the pixel signal by a highconversion gain (first conversion gain) by the change of the capacity(charge quantity) of the floating diffusion FD. At this time, in eachpixel PXL_(n), due to the source-follower transistor SF-Tr, the chargein the floating diffusion FD is converted to a voltage signal inaccordance with the charge quantity (potential). This is output as thereadout signal VSL (HCG21) of column output to the vertical signal lineLSGN, supplied to the readout circuit 40, and for example held.

Here, the first readout period PRD21 ends, and the first transfer periodPT21 starts. Note that, at this time, the capacity changing signalBIN_(n) is held at the L level as it is in a predetermined period afterthe first transfer period PT21 passes up to substantially the timeimmediately before the start of the next second transfer period PT22. Inthe first transfer period PT21, the transfer transistor TG-Tr isselected and becomes a conductive state for the period where the controlline TG is at the H level, and the charge (electrons) which is generatedby photo-electric conversion and accumulated in the photodiode PD istransferred to the floating diffusion FD. After this first transferperiod PT21 passes (the transfer transistor TG-Tr is in a nonconductivestate), the second readout period PRD22 for reading out the pixel signalin accordance with the charge which is generated by photo-electricconversion and accumulated in the photodiode PD starts.

At the time t3 after the second readout period PRD22 is started, in thestate where the capacity changing signal BIN_(n) is set at the L level,the readout portion 70 performs a second high conversion gain modereading operation HCG22 for reading out the pixel signal by a highconversion gain (first conversion gain) resulting from the capacity(charge quantity) of the floating diffusion FD being set to the firstcapacity. At this time, in each pixel PXL_(n), due to thesource-follower transistor SF-Tr, the charge in the floating diffusionFD is converted to a voltage signal in accordance with the chargequantity (potential). This is output as the readout signal VSL (HCG22)of column output to the vertical signal line LSGN, supplied to thereadout circuit 40, and for example held.

In the second readout period PRD22, after the second high conversiongain mode reading operation HCG22 is carried out at the time t3, thecapacity changing signal BIN_(n) is switched to the H level, and thecapacity (charge quantity) of the floating diffusion FD is changed so asto increase from the first capacity to the second capacity.Substantially parallel to this capacity change, the second transferperiod PT22 starts. Note that, at this time, the capacity changingsignal BIN_(n) is held at the H level as it is even after the secondtransfer period PT22 passes. In the second transfer period PT22, thetransfer transistor TG-Tr is selected and becomes a conductive state forthe period where the control line TG is at the H level, and the charge(electrons) which is generated by photo-electric conversion andaccumulated in the photodiode PD is transferred to the floatingdiffusion FD. After this second transfer period PT22 passes (thetransfer transistor TG-Tr is in the nonconductive state), a thirdreadout period PRD23 for further reading out the pixel signal inaccordance with the charge which is generated by photo-electricconversion and accumulated in the photodiode PD starts.

At a time t4 after the third readout period PRD23 is started, in thestate where the capacity changing signal BIN_(n) is held at the H level,the readout portion 70 performs the second low conversion gain modereading operation LCG22 for reading out the pixel signal by a lowconversion gain (second conversion gain) resulting from the capacity(charge quantity) of the floating diffusion FD being set to the secondcapacity. At this time, in each pixel PXL_(n), due to thesource-follower transistor SF-Tr, the charge in the floating diffusionFD is converted to a voltage signal in accordance with the chargequantity (potential). This is output as the readout signal VSL (LCG22)of column output to the vertical signal line LSGN, supplied to thereadout circuit 40, and for example held.

Further, in for example the readout circuit 40 configuring a portion ofthe readout portion 70, a difference {VSL(HCG22)−VSL(HCG21)} between thereadout signal VSL (HCG22) of the second high conversion gain modereading operation HCG22 and the readout signal VSL (HCG21) of the firsthigh conversion gain mode reading operation HCG21 is taken, and CDSprocessing is carried out. In the same way, in the readout circuit 40, adifference {VSL(LCG22)−VSL(LCG21)} between the readout signal VSL(LCG22) of the second low conversion gain mode reading operation LCG22and the readout signal VSL (LCG21) of the first low conversion gain modereading operation LCG21 is taken, and CDS processing is carried out.

Next, as shown in FIG. 11, in order to select the row next to the n-throw in the pixel array, for example the n+1-th row, in place of the n-throw, the control line SEL which is connected to each pixel PXL_(n+1) inthat selected n+1-th row is set at the H level and the selectiontransistor SEL-Tr of the pixel PXL_(n+1) becomes a conductive state. Atthis time, the capacity changing signal BIN_(n) is held at the H levelas it is at the time of access to the n-th row. Further, in thisselection state, in the reset period PR22, all first binning transistors84 _(n), 84 _(n+1) (84 _(n−1) . . . ) are selected and become theconductive state for the period where the capacity changing signalsBIN_(n) and BIN_(n+1) are at the H level as the reset signals, and thefloating diffusions FD are reset to the potential of the power supplyline VDD. After this reset period PR22 passes, the capacity changingsignal BIN_(n+1) is switched to the L level and the first binningtransistor 84 _(n+1) is switched to the nonconductive state. On theother hand, the capacity changing signal BIN_(n) is held at the H levelas it is, and the first binning transistor 84 _(n) is held in theconductive state. The reset period PR22 ends by the first binningtransistor 84 _(n+1) being switched to the nonconductive state and thefirst binning transistor 84 _(n) being held in the conductive state, andthe capacity (charge quantity) of the floating diffusion FD in the pixelPXL_(n+1) is changed so as to increase from the first capacity to thesecond capacity. Further, the period up to the start of the transferperiod PT23 becomes a first readout period PRD24 for reading out thepixel signal at the time of the reset state.

At the time t1 after the first readout period PRD24 is started, in thestate where the capacity changing signal BIN_(n) is held at the H level,the readout portion 70 performs the first low conversion gain modereading operation LCG23 for reading out the pixel signal by a lowconversion gain (second conversion gain) resulting from the capacity(charge quantity) of the floating diffusion FD being changed to thesecond capacity. At this time, in each pixel PXL_(n+1), due to thesource-follower transistor SF-Tr, the charge in the floating diffusionFD is converted to a voltage signal in accordance with the chargequantity (potential). This is output as the readout signal VSL (LCG23)of column output to the vertical signal line LSGN, supplied to thereadout circuit 40, and for example held.

In the first readout period PRD24, after the first low conversion gainmode reading operation LCG23 is carried out at the time t1, the capacitychanging signal BIN_(n) is switched to the L (low level), and thecapacity (charge quantity) of the floating diffusion FD is changed so asto decrease from the second capacity to the first capacity. Further, atthe time t2, the readout portion 70 performs a first high conversiongain mode reading operation HCG23 for reading out the pixel signal by ahigh conversion gain (first conversion gain) by the change of thecapacity (charge quantity) of the floating diffusion FD. At this time,in each pixel PXL_(n+1), due to the source-follower transistor SF-Tr,the charge in the floating diffusion FD is converted to a voltage signalin accordance with the charge quantity (potential). This is output asthe readout signal VSL (HCG23) of column output to the vertical signalline LSGN, supplied to the readout circuit 40, and for example held.

Here, the first readout period PRD24 ends, and the first transfer periodPT23 starts. Note that, at this time, the capacity changing signalBIN_(n) is held at the L level as it is in a predetermined period afterthe first transfer period PT23 passes up to substantially the timeimmediately before the start of the next second transfer period PT24. Inthe first transfer period PT23, the transfer transistor TG-Tr isselected and becomes a conductive state for the period where the controlline TG is at the high level (H), and the charge (electrons) which isgenerated by photo-electric conversion and accumulated in the photodiodePD is transferred to the floating diffusion FD. After this firsttransfer period PT23 passes (the transfer transistor TG-Tr is in anonconductive state), a second readout period PRD25 for reading out thepixel signal in accordance with the charge which is generated byphoto-electric conversion and accumulated in the photodiode PD starts.

At the time t3 after the second readout period PRD25 is started, in thestate where the capacity changing signal BIN_(n) is set at the L level,the readout portion 70 performs a second high conversion gain modereading operation HCG24 for reading out the pixel signal by a highconversion gain (first conversion gain) resulting from the capacity(charge quantity) of the floating diffusion FD being set to the firstcapacity. At this time, in each pixel PXL_(n+1), due to thesource-follower transistor SF-Tr, the charge in the floating diffusionFD is converted to a voltage signal in accordance with the chargequantity (potential). This is output as the readout signal VSL (HCG24)of column output to the vertical signal line LSGN, supplied to thereadout circuit 40, and for example held.

In the second readout period PRD25, after the second high conversiongain mode reading operation HCG24 is carried out at the time t3, thecapacity changing signal BIN_(n) is switched to the H level, and thecapacity (charge quantity) of the floating diffusion FD is changed so asto increase from the first capacity to the second capacity.Substantially parallel to this capacity change, the second transferperiod PT24 starts. Note that, at this time, the capacity changingsignal BIN_(n) is held at the H level as it is even after the secondtransfer period PT24 passes. In the second transfer period PT24, thetransfer transistor TG-Tr is selected and becomes a conductive state forthe period where the control line TG is at the high level (H), and thecharge (electrons) which is generated by photo-electric conversion andaccumulated in the photodiode PD is transferred to the floatingdiffusion FD. After this second transfer period PT24 passes (thetransfer transistor TG-Tr is in the nonconductive state), a thirdreadout period PRD26 for further reading out the pixel signal inaccordance with the charge which is generated by photo-electricconversion and accumulated in the photodiode PD starts.

At the time t4 after the third readout period PRD26 is started, in thestate where the capacity changing signal BIN_(n) is held at the H level,the readout portion 70 performs the second low conversion gain modereading operation LCG24 for reading out the pixel signal by a lowconversion gain (second conversion gain) resulting from the capacity(charge quantity) of the floating diffusion FD being set to the secondcapacity. At this time, in each pixel PXL_(n+1), due to thesource-follower transistor SF-Tr, the charge in the floating diffusionFD is converted to a voltage signal in accordance with the chargequantity (potential). This is output as the readout signal VSL (LCG24)of column output to the vertical signal line LSGN, supplied to thereadout circuit 40, and for example held.

Further, in for example the readout circuit 40 configuring a portion ofthe readout portion 70, a difference {VSL(HCG24)−VSL(HCG23)} between thereadout signal VSL (HCG24) of the second high conversion gain modereading operation HCG24 and the readout signal VSL (HCG23) of the firsthigh conversion gain mode reading operation HCG23 is taken, and CDSprocessing is carried out. In the same way, in the readout circuit 40, adifference {VSL(LCG24)−VSL(LCG23)} between the readout signal VSL(LCG24) of the second low conversion gain mode reading operation LCG24and the readout signal VSL (LCG23) of the first low conversion gain modereading operation LCG23 is taken, and CDS processing is carried out.

According to the third embodiment, effects the same as those by thefirst and second embodiments explained above can be obtained. That is,according to the third embodiment, the following effects can beobtained: With respect to the charge (electrons) which is generated byphoto-electric conversion in one accumulation period (exposure period),inside the pixel, in one readout period, signals are output by switchingthe high conversion gain mode and the low conversion gain mode so bothof the bright signal and dark signal can be output, a reset noise at thetime of high conversion gain mode and low conversion gain mode can becancelled, dynamic range widening can be realized while suppressingoccurrence of motion distortion, and consequently a higher image qualitycan be realized.

Further, according to the third embodiment, it is possible to flexiblyswitch the number of connections of the floating diffusions FD, so theexpandability of the dynamic range is excellent. Further, the number oftransistors inside a pixel is small, therefore the aperture ratio of thePD is high, and the photo-electric conversion sensitivity and the numberof saturated electrons can be raised. Further, according to the thirdembodiment, provision is made of pixels where a reset element is sharedby two pixels in one column. Therefore, at the time of reset of thefloating diffusion FD, the resistance between the floating diffusion FDand the reset electrode is low, so there is the advantage of excellentspeed in the reset operation.

Further, according to the third embodiment, the readout portion 70,during the readout scan period PRDO, sets a plurality of (two in thepresent example) transfer periods for performing the transfer processingand performs processing of reading out the signal in accordance with theaccumulated charge in each readout period after each transfer period,therefore it becomes possible to reliably realize further widening ofdynamic range. Further, according to the third embodiment, the readoutportion 70, in at least one transfer period (transfer period on thelatter stage side in the present example) among the plurality oftransfer periods, transfers the accumulated charge from thephoto-electric conversion element PD in a state where the capacity ofthe floating diffusion is made large by the capacity changing portion,therefore it becomes possible to reduce an overflowing charge, theaccumulated charge can be effectively utilized, and consequently ahigher image quality can be realized.

Fourth Embodiment

FIG. 12 is a diagram showing an example of the configuration of a pixelportion and capacity changing portion according to a fourth embodimentof the present invention.

The difference of a capacity changing portion 80D in the fourthembodiment from the capacity changing portion 80C in the thirdembodiment is as follows.

In the third embodiment described above, the reset element is shared bythe two adjacent pixels PXL_(n) and PXL_(n+1) in one column, thefloating diffusion FD in the pixel PXL_(n) and the power supply line VDDare connected to each other through the first binning transistors(switches) 84 _(n) and 84 _(n+1) which are formed so as to be cascadeconnected to the wiring WR, and the connection node ND_(n+1) of thefirst binning transistors (switches) 84 _(n) and 84 _(n+1) which islocated on the wiring WR and the floating diffusion FD in the pixelPXL_(n+1) are connected. In the third embodiment, the first binningtransistor (switch) 84 _(n+1) functions as the shared reset element.

Contrary to this, in the fourth embodiment, the reset element is sharedby all pixels . . . PXL_(n−1), PXL_(n), PXL_(n+1) . . . in one column,for example the floating diffusion FD in a pixel PXL₀ (not shown in FIG.12) on one end of one column and the power supply line VDD (not shown inFIG. 12) which is formed close to a pixel PXL_(N−1) on the other end ofone column are connected to each other through the first binningtransistors (switches) . . . 84 _(n−1), 84 _(n), 84 _(n+1) . . . whichare formed so as to be cascade connected to the wiring WR whilecorresponding to the pixels, and nodes . . . ND_(n−1), ND_(n), ND_(n+1). . . on the wiring WR among the first binning switches and the floatingdiffusions FD of the corresponding pixels . . . PXL_(n−1), PXL_(n),PXL_(n+1) . . . are connected. In the fourth embodiment, the not shownfirst binning transistor (switch) 84 _(N−1) which is nearest the otherend functions as the shared reset element.

By such a configuration, according to the fourth embodiment, it ispossible to flexibly switch the number of connections of floatingdiffusions FD, so the expandability of the dynamic range is excellent.Further, the number of transistors inside a pixel is small, thereforethe aperture ratio of a PD is high, and the photo-electric conversionsensitivity and the number of saturated electrons can be raised.

Next, the operation for realizing a wide dynamic range in a case where abinning switch (binning transistor) is applied to the capacity changingportion according to the fourth embodiment will be explained withreference to FIG. 13.

FIG. 13 is a timing chart for explaining the operation for realizing awide dynamic range where a binning switch (binning transistor) isapplied to the capacity changing portion according to the fourthembodiment.

In the fourth embodiment, a non-reset state is set by making thecapacity changing signals corresponding to the pixels on the two ends ofthe column output direction of the readout pixels the L level. Forexample, a non-reset state is set by making the capacity changingsignals BIN_(n−1) and BIN_(n+1) corresponding to the pixels PXL_(n−1)and PXL_(n+1) on the two ends in the column output direction of thereadout pixels PXL_(n) the L level. Further, for example, a non-resetstate is set by making the capacity changing signals BIN_(n) andBIN_(n+2) (not shown) corresponding to the pixels PXL_(n) and PXL_(n+2)(not shown) on the two ends in the column output direction of thereadout pixel PXL_(n+1) the L level.

Note, this is one example. In a case of increasing the number of thefloating diffusions to be connected, a non-reset state is set not bymaking the capacity changing signals BIN corresponding to the pixelswhich are exactly adjacent the L level, but by making the capacitychanging signals BIN corresponding to the pixels separated by aplurality of (two or more) rows the L level according to the mode ofconnection.

During the readout scan period PRDO, as shown in FIG. 13, in order toselect one row in the pixel array, for example the n-th row, a controlline SEL which is connected to each pixel PXL_(n) in that selected rowis set at the H level whereby the selection transistor SEL-Tr in thepixel PXL_(n) becomes a conductive state. In this selection state, in areset period PR31, all first binning transistors 84 _(n−1), 84 _(n), and84 _(n+1) are selected and become the conductive state for the periodwhere the capacity changing signals BIN_(n−1), BIN_(n), and BIN_(n+1)are at the H level as the reset signals, and the floating diffusions FDare reset to the potential of the power supply line VDD. After thisreset period PR31 passes, the capacity changing signals BIN_(n−1) andBIN_(n+1) are switched to the L level and the first binning transistors84 _(n−1) and 84 _(n+1) are switched to the nonconductive state. On theother hand, the capacity changing signal BIN_(n) is held at the H levelas it is and the first binning transistor 84 _(n) is held in theconductive state. The reset period PR31 ends by the first binningtransistors 84 _(n−1) and 84 _(n+1) being switched to the nonconductivestate and the first binning transistor 84 _(n) being held in theconductive state, and the capacity (charge quantity) of the floatingdiffusion FD in the pixel PXL_(n) is changed so as to increase from thefirst capacity to the second capacity. Further, the period up to thestart of the transfer period PT31 becomes the first readout period PRD31for reading out the pixel signal at the time of the reset state.

At the time t1 after the first readout period PRD31 is started, in thestate where the capacity changing signal BIN_(n) is held at the H level,the readout portion 70 performs a first low conversion gain mode readingoperation LCG31 for reading out the pixel signal by a low conversiongain (second conversion gain) resulting from the capacity (chargequantity) of the floating diffusion FD being changed to the secondcapacity. At this time, in each pixel PXL_(n), due to thesource-follower transistor SF-Tr, the charge in the floating diffusionFD is converted to voltage signal in accordance with the charge quantity(potential). This is output as the readout signal VSL (LCG31) of columnoutput to the vertical signal line LSGN, supplied to the readout circuit40, and for example held.

In the first readout period PRD31, after the first low conversion gainmode reading operation LCG31 is carried out at the time t1, the capacitychanging signal BIN_(n) is switched to L (low level), and the capacity(charge quantity) of the floating diffusion FD is changed so as todecrease from the second capacity to the first capacity. Further, at thetime t2, the readout portion 70 performs the first high conversion gainmode reading operation HCG31 for reading out the pixel signal by a highconversion gain (first conversion gain) resulting from the capacity(charge quantity) of the floating diffusion FD being changed. At thistime, in each pixel PXL_(n), due to the source-follower transistorSF-Tr, the charge in the floating diffusion FD is converted to a voltagesignal in accordance with the charge quantity (potential). This isoutput as the readout signal VSL (HCG31) of column output to thevertical signal line LSGN, supplied to the readout circuit 40, and forexample held.

Here, the first readout period PRD31 ends, and the first transfer periodPT31 starts. Note that, at this time, the capacity changing signalBIN_(n) is held at the L level as it is in a predetermined period afterthe first transfer period PT31 passes up to substantially the timeimmediately before the start of the next second transfer period PT32. Inthe first transfer period PT31, the transfer transistor TG-Tr isselected and becomes a conductive state for the period where the controlline TG is at the H level, and the charge (electrons) which is generatedby photo-electric conversion and accumulated in the photodiode PD istransferred to the floating diffusion FD. After this first transferperiod PT31 passes (the transfer transistor TG-Tr is in thenonconductive state), the second readout period PRD32 for reading outthe pixel signal in accordance with the charge which is generated byphoto-electric conversion and accumulated in the photodiode PD starts.

At the time t3 after the second readout period PRD32 is started, in thestate where the capacity changing signal BIN_(n) is set at the L level,the readout portion 70 performs the second high conversion gain modereading operation HCG32 for reading out the pixel signal by a highconversion gain (first conversion gain) resulting from the capacity(charge quantity) of the floating diffusion FD being set to the firstcapacity. At this time, in each pixel PXL_(n), due to thesource-follower transistor SF-Tr, the charge in the floating diffusionFD is converted to a voltage signal in accordance with the chargequantity (potential). This is output as the readout signal VSL (HCG32)of column output to the vertical signal line LSGN, supplied to thereadout circuit 40, and for example held.

During the second readout period PRD32, after the second high conversiongain mode reading operation HCG32 is carried out at the time t3, thecapacity changing signal BIN_(n) is switched to the H level to changethe capacity so that the capacity (charge quantity) of the floatingdiffusion FD increases from the first capacity to the second capacity.Substantially parallel to this capacity change, the second transferperiod PT32 starts. Note that, at this time, the capacity changingsignal BIN_(n) is held at the H level as it is even after the secondtransfer period PT32 passes. In the second transfer period PT32, thetransfer transistor TG-Tr is selected and becomes conductive state forthe period where the control line TG is at the high level H, and thecharge (electrons) which is generated by photo-electric conversion andaccumulated in the photodiode PD is transferred to the floatingdiffusion FD. After this second transfer period PT32 passes (thetransfer transistor TG-Tr is in the nonconductive state), a thirdreadout period PRD33 for further reading out the pixel signal inaccordance with the charge which is generated by photo-electricconversion and accumulated in the photodiode PD starts.

At the time t4 after the third readout period PRD33 is started, in thestate where the capacity changing signal BIN_(n) is held at the H level,the readout portion 70 performs the second low conversion gain modereading operation LCG32 for reading out the pixel signal by a lowconversion gain (second conversion gain) resulting from the capacity(charge quantity) of the floating diffusion FD being set to the secondcapacity. At this time, in each pixel PXL_(n), due to thesource-follower transistor SF-Tr, the charge in the floating diffusionFD is converted to a voltage signal in accordance with the chargequantity (potential). This is output as the readout signal VSL (LCG32)of column output to the vertical signal line LSGN, supplied to thereadout circuit 40, and for example held.

Further, in for example the readout circuit 40 configuring a portion ofthe readout portion 70, a difference {VSL(HCG32)−VSL(HCG31)} between thereadout signal VSL (HCG32) of the second high conversion gain modereading operation HCG32 and the readout signal VSL (HCG31) of the firsthigh conversion gain mode reading operation HCG31 is taken, and CDSprocessing is carried out. In the same way, in the readout circuit 40, adifference {VSL(LCG32)−VSL(LCG31)} between the readout signal VSL(LCG32) of the second low conversion gain mode reading operation LCG32and the readout signal VSL (LCG31) of the first low conversion gain modereading operation LCG31 is taken, and CDS processing is carried out.

Next, as shown in FIG. 13, in order to select the row next to the n-throw in the pixel array, for example the n+1-th row, in place of the n-throw, the control line SEL which is connected to each PXL_(n+1) in thatselected n+1-th row is set at the H level and the selection transistorSEL-Tr in the pixel PXL_(n+1) becomes a conductive state. At this time,the capacity changing signal BIN_(n) is held at the H level at the timeof access to the n-th row as it is. Further, in this selection state, inthe reset period PR32, all first binning transistors 84 _(n−1), 84 _(n),and 84 _(n+1) are selected and become the conductive state for theperiod where the capacity changing signals BIN_(n−1), BIN_(n), andBIN_(n+1) are at the H level as the reset signals, and the floatingdiffusions FD are reset to the potential of the power supply line VDD.After this reset period PR32 passes, the capacity changing signalBIN_(n) is switched to the L level and the first binning transistor 84_(n) is switched to the nonconductive state. On the other hand, thecapacity changing signals BIN_(n+1) and BIN⁻¹ are held at the H level asthey are and the first binning transistors 84 _(n+1) and BIN_(n−1) areheld in the conductive state. The reset period PR32 ends by the firstbinning transistor 84 _(n) being switched to the nonconductive state andthe first binning transistors 84 _(n+1) and 84 ⁻¹ being held in theconductive state, and the capacity (charge quantity) of the floatingdiffusion FD in the pixel PXL_(n+1) is changed so as to increase fromthe first capacity to the second capacity. Further, the period up to thestart of the transfer period PT33 becomes a first readout period PRD34for reading out the pixel signal at the time of the reset state.

At the time t1 after the first readout period PRD34 is started, in thestate where the capacity changing signal BIN_(n+1) is held at the Hlevel, the readout portion 70 performs a first low conversion gain modereading operation LCG33 for reading out the pixel signal by a lowconversion gain (second conversion gain) resulting from the capacity(charge quantity) of the floating diffusion FD being changed to thesecond capacity. At this time, in each pixel PXL_(n+1), due to thesource-follower transistor SF-Tr, the charge in the floating diffusionFD is converted to a voltage signal in accordance with the chargequantity (potential). This is output as the readout signal VSL (LCG33)of column output to the vertical signal line LSGN, supplied to thereadout circuit 40, and for example held.

In the first readout period PRD34, after the first low conversion gainmode reading operation LCG33 is carried out at the time t1, the capacitychanging signal BIN_(n+1) is switched to L (low level), and the capacity(charge quantity) of the floating diffusion FD is changed so as todecrease from the second capacity to the first capacity. Further, at thetime t2, the readout portion 70 performs the first high conversion gainmode reading operation HCG33 for reading out the pixel signal by a highconversion gain (first conversion gain) resulting from the capacity(charge quantity) of the floating diffusion FD being changed. At thistime, in each pixel PXL_(n+1), due to the source-follower transistorSF-Tr, the charge in the floating diffusion FD is converted to a voltagesignal in accordance with the charge quantity (potential). This isoutput as the readout signal VSL (HCG33) of column output to thevertical signal line LSGN, supplied to the readout circuit 40, and forexample held.

Here, the first readout period PRD34 ends, and the first transfer periodPT33 starts. Note that, at this time, the capacity changing signalBIN_(n+1) is held at the L level as it is in a predetermined periodafter the first transfer period PT33 passes up to substantially the timeimmediately before the start of the next second transfer period PT34. Inthe first transfer period PT33, the transfer transistor TG-Tr isselected and becomes a conductive state for the period where the controlline TG is at the H level, and the charge (electrons) which is generatedby photo-electric conversion and accumulated in the photodiode PD istransferred to the floating diffusion FD. After this first transferperiod PT33 passes (the transfer transistor TG-Tr is in thenonconductive state), a second readout period PRD35 for reading out thepixel signal in accordance with the charge which is generated byphoto-electric conversion and accumulated in the photodiode PD starts.

At the time t3 after the second readout period PRD35 is started, in thestate where the capacity changing signal BIN_(n+1) is set at the Llevel, the readout portion 70 performs the second high conversion gainmode reading operation HCG34 for reading out the pixel signal by a highconversion gain (first conversion gain) resulting from the capacity(charge quantity) of the floating diffusion FD being set to the firstcapacity. At this time, in each pixel PXL_(n+1), due to thesource-follower transistor SF-Tr, the charge in the floating diffusionFD is converted to a voltage signal in accordance with the chargequantity (potential). This is output as the readout signal VSL (HCG34)of column output to the vertical signal line LSGN, supplied to thereadout circuit 40, and for example held.

During the second readout period PRD35, after the second high conversiongain mode reading operation HCG34 is carried out at the time t3, thecapacity changing signal BIN_(n+1) is switched to the H level to changethe capacity so that the capacity (charge quantity) of the floatingdiffusion FD increases from the first capacity to the second capacity.Substantially parallel to this capacity change, the second transferperiod PT34 starts. Note that, at this time, the capacity changingsignal BIN_(n+1) is held at the H level as it is even after the secondtransfer period PT34 passes. In the second transfer period PT34, thetransfer transistor TG-Tr is selected and becomes a conductive state forthe period where the control line TG is at the H level, and the charge(electrons) which is generated by photo-electric conversion andaccumulated in the photodiode PD is transferred to the floatingdiffusion FD. After this second transfer period PT34 passes (thetransfer transistor TG-Tr is in the nonconductive state), a thirdreadout period PRD36 for further reading out the pixel signal inaccordance with the charge which is generated by photo-electricconversion and accumulated in the photodiode PD starts.

At the time t4 after the third readout period PRD36 is started, in thestate where the capacity changing signal BIN_(n+1) is held at the Hlevel, the readout portion 70 performs the second low conversion gainmode reading operation LCG34 for reading out the pixel signal by a lowconversion gain (second conversion gain) resulting from the capacity(charge quantity) of the floating diffusion FD being set to the secondcapacity. At this time, in each pixel PXL_(n), due to thesource-follower transistor SF-Tr, the charge in the floating diffusionFD is converted to a voltage signal in accordance with the chargequantity (potential). This is output as the readout signal VSL (LCG34)of column output to the vertical signal line LSGN, supplied to thereadout circuit 40, and for example held.

Further, in for example the readout circuit 40 configuring a portion ofthe readout portion 70, a difference {VSL(HCG34)−VSL(HCG33)} between thereadout signal VSL (HCG34) of the second high conversion gain modereading operation HCG34 and the readout signal VSL (HCG33) of the firsthigh conversion gain mode reading operation HCG33 is taken, and CDSprocessing is carried out. In the same way, in the readout circuit 40, adifference {VSL(LCG34)−VSL(LCG33)} between the readout signal VSL(LCG34) of the second low conversion gain mode reading operation LCG34and the readout signal VSL (LCG33) of the first low conversion gain modereading operation LCG33 is taken, and CDS processing is carried out.

According to the fourth embodiment, effects same as those by the firstand second embodiments explained above can be obtained. That is,according to the fourth embodiment, the following effects can beobtained: With respect to the charge (electrons) which is generated byphoto-electric conversion in one accumulation period (exposure period),inside the pixel, in one readout period, signals are output by switchingthe high conversion gain mode and the low conversion gain mode so bothof the bright signal and dark signal can be output, a reset noise at thetime of high conversion gain mode and low conversion gain mode can becancelled, dynamic range widening can be realized while suppressingoccurrence of motion distortion, and consequently a higher image qualitycan be realized.

Further, according to the fourth embodiment, it is possible to flexiblyswitch the number of connections of the floating diffusions FD, so theexpandability of the dynamic range is excellent. Further, the number oftransistors inside a pixel is small, therefore the aperture ratio of thePD is high, and the photo-electric conversion sensitivity and the numberof saturated electrons can be raised.

Further, according to the fourth embodiment, the readout portion 70,during the readout scan period PRDO, sets a plurality of (two in thepresent example) transfer periods for performing the transfer processingand performs processing of reading out the signal in accordance with theaccumulated charge in each readout period after each transfer period,therefore it becomes possible to reliably realize further widening ofdynamic range. Further, according to the fourth embodiment, the readoutportion 70, in at least one transfer period (transfer period on thelatter stage side in the present example) among the plurality oftransfer periods, transfers the accumulated charge from thephoto-electric conversion element PD in a state where the capacity ofthe floating diffusion is made large by the capacity changing portion,therefore it becomes possible to reduce an overflowing charge, theaccumulated charge can be effectively utilized, and consequently ahigher image quality can be realized.

Fifth Embodiment

FIG. 14 is a diagram showing an example of the configuration of a pixelportion and capacity changing portion according to a fifth embodiment ofthe present invention.

The difference of a capacity changing portion 80E in the fifthembodiment from the capacity changing portion 80D in the fourthembodiment is as follows. In the fifth embodiment, in addition to thefirst binning transistors (binning switches) 84 _(n−1), 84 _(n), and 84_(n+1) which are formed so as to be cascade connected on the wiring WRand correspond to the pixels, for example, second binning transistors(binning switches) 85 _(n−1), 85 _(n), and 85 _(n+1) which are formed byNMOS transistors are connected between the floating diffusions FD of thepixels PXL_(n−1), PXL_(n), and PXL_(n+1), and the nodes ND_(n−1),ND_(n), and ND_(n+1) of the wiring WR.

The first binning transistors 84 _(n−1), 84 _(n), and 84 _(n+1) areselectively turned ON or OFF by the first capacity changing signals BIN1_(n−1), BIN1 _(n), and BIN1 _(n+1), and the second binning transistors85 _(n−1), 85 _(n), and 85 _(n+1) are selectively turned ON or OFF bythe second capacity changing signals BIN2 _(n−1), BIN2 _(n), and BIN2_(n+1). In the present embodiment, as shown in FIG. 15, the firstcapacity changing signals BIN1 _(n−1), BIN1 _(n), and BIN1 _(n+1) andthe second capacity changing signals BIN2 _(n−1), BIN2 _(n), and BIN2_(n+1) form pairs and are switched to the H level or L level at the sametiming (with the same phase).

In such a configuration, the first binning transistors 84 _(n−1), 84_(n), and 84 _(n+1) are used for connection and disconnection of theadjacent FD wirings WR. The second binning transistors 85 _(n−1), 85_(n), and 85 _(n+1) are arranged in the vicinity of the transfertransistors TG-Tr in the pixels PXL_(n−1), PXL_(n), and PXL_(n+1). Inthe high conversion gain mode, they are used for minimizing theparasitic capacitance of a floating diffusion FD node.

FIG. 15 is a timing chart of the operation for realizing a wide dynamicrange in a case where the binning switches are applied to the capacitychanging portion according to the fifth embodiment. The operation of thefifth embodiment is basically the same as the operation in the fourthembodiment explained before except that the first and second capacitychanging signals BIN1 _(n+1) and BIN2 _(n+1) of the read out pixel, forexample the pixel PXL_(n+1) which is adjacent to the upper side of thepixel PXL_(n) are switched to the H level or L level at the same timing(with the same phase) as that for the first and second capacity changingsignals BIN1 _(n) and BIN2 _(n) of the readout pixel PXL_(n).Accordingly, details of the operation of the fifth embodiment willomitted.

According to the fifth embodiment, the same effects as those by thefourth embodiment explained above can be obtained. That is, according tothe fifth embodiment, the following effects can be obtained: Withrespect to the charge (electrons) which is generated by photo-electricconversion in one accumulation period (exposure period), inside thepixel, in one readout period, signals are output by switching the highconversion gain mode and the low conversion gain mode so both of thebright signal and dark signal can be output, a reset noise at the timeof high conversion gain mode and low conversion gain mode can becancelled, dynamic range widening can be realized while suppressingoccurrence of motion distortion, and consequently a higher image qualitycan be realized. Further, according to the fifth embodiment, it ispossible to flexibly switch the number of connections of the floatingdiffusions FD, so the expandability of the dynamic range is excellent.Further, the number of transistors in a pixel is small, therefore theaperture ratio of the PD is high, and the photo-electric conversionsensitivity and the number of saturated electrons can be raised.

Further, according to the fifth embodiment, in the high conversion gainmode, the parasitic capacitance of a floating diffusion FD node can beminimized.

Further, according to the fifth embodiment, the readout portion 70,during the readout scan period PRDO, sets a plurality of (two in thepresent example) transfer periods for performing the transfer processingand performs the processing of reading out the signal in accordance withthe accumulated charges in each readout period after each transferperiod, therefore it becomes possible to reliably realize a furtherwidening of dynamic range. Further, according to the fifth embodiment,the readout portion 70, in at least one transfer period (transfer periodon the latter stage side in the present example) among the plurality oftransfer periods, transfers the accumulated charge from thephoto-electric conversion element PD in a state where the capacity ofthe floating diffusion is made large by the capacity changing portion,therefore it becomes possible to reduce an overflowing charge, theaccumulated charge can be effectively utilized, and consequently ahigher image quality can be realized.

Sixth Embodiment

FIG. 16 is a diagram showing an example of the configuration of a pixelportion and capacity changing portion according to a sixth embodiment ofthe present invention. FIG. 17 is a timing chart of the operation forrealizing a wide dynamic range in a case where a binning switch isapplied to the capacity changing portion according to the sixthembodiment.

The difference of a capacity changing portion 80F in the sixthembodiment from the capacity changing portion 80E in the fifthembodiment is as follows. In the sixth embodiment, in the pixelsPXL_(n−1), PXL_(n), and PXL₊₁, between the connection portions of thefirst binning transistors 84 _(n−1), 84 _(n), and 84 _(n+1) with theupper side adjacent pixels, and the power supply line VDD, overflowdrain (OFD) gates 86 _(n−1), 86 _(n), and 86 _(n+1) are connected.

The OFD gates 86 _(n−1), 86 _(n), and 86 _(n+1) discharge the overflowelectrons to the power supply line (terminals) so that the electrons(charge) which overflow from the photodiodes PD to the floatingdiffusions FD at the time of high brightness are not leaked to theadjacent pixels.

Further, by setting the voltages of OFD gates 86 _(n−1), 86 _(n), and 86_(n+1) higher than the voltages at L level of the first capacitychanging signals BIN1 _(n−1), BIN1 _(n), and BIN1 _(n+1) and secondcapacity changing signals BIN2 _(n−1), BIN2 _(n), and BIN2 _(n+1), areduction of the potentials of the floating diffusions FD in theadjacent pixels due to the electrons (charge) overflowing from thephotodiodes PD can be prevented.

Further, as shown in FIG. 17, the OFD gates 86 _(n−1), 86 _(n), and 86_(n+1) may be used for reset as well. In contrast to the configurationof providing a reset element and binning switch, the number of elementswhich are connected to the floating diffusion FD node is smaller,therefore the characteristics at the time of high conversion gain areexcellent.

Example of Application

FIG. 18 is a diagram for explaining that the solid-state imaging deviceaccording to the embodiment of the present invention can be applied toalso a pixel sharing structure.

The solid-state imaging device 10 in the present embodiment explainedabove, as shown in FIG. 18, can be applied to also a pixel sharingstructure in which one floating diffusion FD is shared by a plurality of(four in the example of FIG. 18) photodiodes PDa, PDb, PDc, and PDd.

FIG. 19A and FIG. 19B are diagrams for explaining the fact that thesolid-state imaging device according to an embodiment of the presentinvention can be applied to both of a front-surface irradiation typeimage sensor and a back-surface irradiation type image sensor: FIG. 19Ashows a simplified configuration of the front-surface irradiation typeimage sensor, and FIG. 19B shows a simplified configuration of theback-surface irradiation type image sensor.

In FIG. 19, notation 91 indicates a microlens array, 92 indicates acolor filter group, 93 indicates a wiring layer, and 94 indicates asilicon substrate.

The solid-state imaging device 10 in the present embodiment explainedabove, as shown in FIG. 19A and FIG. 19B, can be applied to both of afront-surface irradiation type image sensor (FSI) and back-surfaceirradiation type image sensor (BSI).

The solid-state imaging device 10 explained above can be applied as animaging device to a digital camera or video camera, portable terminal,or monitoring camera, medical endoscope, or other electronic apparatus.

FIG. 20 is a diagram showing an example of the configuration of anelectronic apparatus having a camera system to which a solid-stateimaging device according to an embodiment of the present invention isapplied mounted therein.

The electronic apparatus 100, as shown in FIG. 20, has a CMOS imagesensor 110 to which the solid-state imaging device 10 according to thepresent embodiment can be applied. Further, the electronic apparatus 100has an optical system (lens etc.) 120 for guiding the incident light tothe pixel region of this CMOS image sensor 110 (forming an objectimage). The electronic apparatus 100 has a signal processing circuit(PRC) 130 for processing the output signal of the CMOS image sensor 110.

The signal processing circuit 130 applies predetermined signalprocessing to the output signal of the CMOS image sensor 110. The imagesignal which is processed in the signal processing circuit 130 can beprojected as a moving picture on a monitor configured by a liquidcrystal display or the like or can be output to a printer. Further, forexample, it can be directly stored in a memory card or other storagemedium. Various aspects are possible.

As explained above, by mounting the solid-state imaging device 10explained before as the CMOS image sensor 110, it becomes possible toprovide a high performance, small-sized, and low cost camera system.Further, an electronic apparatus used for applications restricted in themounting size, number of cables which can be connected, length of thecables, or set heights as requirements of camera installation, forexample, a monitoring camera or medical endoscope, can be realized.

The invention claimed is:
 1. A solid-state imaging device comprising apixel portion in which pixels are arranged, wherein each pixel includesa photo-electric conversion element which accumulates a charge generatedby photo-electric conversion in an accumulation period, a transferelement capable of transferring the charge accumulated in thephoto-electric conversion element in a transfer period, a floatingdiffusion to which the charge accumulated in the photo-electricconversion element is transferred through the transfer element, asource-follower element which converts the charge of the floatingdiffusion to a voltage signal by a gain in accordance with the chargequantity, and a capacity changing portion capable of changing thecapacity of the floating diffusion in accordance with a capacitychanging signal, wherein the capacity of the floating diffusion ischanged by the capacity changing portion in a predetermined period inone readout period with respect to the accumulation period and aconversion gain is switched in the one readout period, and wherein thecapacity changing portion includes a MOS structure capacitor connectedto the floating diffusion, the MOS structure capacitor is changed ingate voltage by the capacity changing signal to change the capacity ofthe floating diffusion and switch the conversion gain of the floatingdiffusion; the solid-state imaging device further comprising a readoutportion for reading out a pixel signal from the pixel portion, whereineach pixel includes a reset element which discharges the charge of thefloating diffusion in a reset period, and the readout portion canperform, in one the readout period with respect to the accumulationperiod, a first conversion gain mode reading operation for reading out apixel signal by a first conversion gain in accordance with a firstcapacity which is set by the capacity changing portion and a secondconversion gain mode reading operation for reading out a pixel signal bya second conversion gain in accordance with a second capacity which isset by the capacity changing portion, performs a first operation of thefirst conversion gain mode reading operation in a first readout periodfollowing the reset period, then performs a first operation of thesecond conversion gain mode reading operation, performs transferprocessing for the transfer period by the transfer element after thefirst readout period in a state where the capacity of the floatingdiffusion is held at the second capacity corresponding to the secondconversion gain, and performs a second operation of the secondconversion gain mode reading operation in a second readout period afterthe transfer period, then performs a second operation of the firstconversion gain mode reading operation.
 2. A solid-state imaging deviceas set forth in claim 1, wherein the MOS structure capacitor is formedby a first conductivity type MOS, one diffusion layer connected to thefloating diffusion is a first conductivity type, and the other diffusionlayer not connected to the floating diffusion is a second conductivitytype.
 3. A solid-state imaging device as set forth in claim 1, whereinthe MOS structure capacitor has a buried channel structure.
 4. Asolid-state imaging device as set forth in claim 1, wherein the secondcapacity is larger than the first capacity.
 5. A solid-state imagingdevice as set forth in claim 1, wherein the pixel portion has a pixelshared structure where one the floating diffusion is shared by aplurality of the photo-electric conversion elements and the transferelements.
 6. A solid-state imaging device as set forth in claim 1,wherein the solid-state imaging device is a front-surface irradiationtype or back-surface irradiation type.
 7. A method for driving asolid-state imaging device having a pixel portion in which pixels arearranged, wherein each pixel includes a photo-electric conversionelement which accumulates a charge generated by photo-electricconversion in an accumulation period, a transfer element capable oftransferring the charge accumulated in the photo-electric conversionelement in a transfer period, a floating diffusion to which the chargesaccumulated in the photo-electric conversion element is transferredthrough the transfer element, a source-follower element which convertsthe charge of the floating diffusion to a voltage signal by a gain inaccordance with the charge quantity, a capacity changing portion capableof changing the capacity of the floating diffusion in accordance with acapacity changing signal, and a reset element which discharges thecharge of the floating diffusion in a reset period, comprising changingthe capacity of the floating diffusion by the capacity changing portionin the predetermined period in one readout period with respect to theaccumulation period and switching a conversion gain in the one readoutperiod, the method for driving a solid-state imaging device comprisingforming the capacity changing portion by a MOS structure capacitorconnected to the floating diffusion, changing gate voltage of the MOSstructure capacitor by the capacity changing signal to change thecapacity of the floating diffusion and switch the conversion gain of thefloating diffusion, performing, in one the readout period with respectto the accumulation period, a first conversion gain mode readingoperation for reading out a pixel signal by a first conversion gain inaccordance with a first capacity which is set by the capacity changingportion and a second conversion gain mode reading operation for readingout a pixel signal by a second conversion gain in accordance with asecond capacity which is set by the capacity changing portion,performing a first operation of the first conversion gain mode readingoperation in a first readout period following the reset period, thenperforming a first operation of the second conversion gain mode readingoperation, performing transfer processing for the transfer period by thetransfer element after the first readout period in a state where thecapacity of the floating diffusion is held at the second capacitycorresponding to the second conversion gain, and performing a secondoperation of the second conversion gain mode reading operation in asecond readout period after the transfer period, then performing asecond operation of the first conversion gain mode reading operation. 8.An electronic apparatus comprising a solid-state imaging device whichincludes a pixel portion in which pixels are arranged and an opticalsystem which forms an object image at the solid-state imaging device,wherein each pixel of the solid-state imaging device includes, aphoto-electric conversion element which accumulates a charge generatedby photo-electric conversion in an accumulation period, a transferelement capable of transferring the charge accumulated in thephoto-electric conversion element in a transfer period, a floatingdiffusion to which the charge accumulated in the photo-electricconversion element is transferred through the transfer element, asource-follower element which converts the charge of the floatingdiffusion to a voltage signal by a gain in accordance with the chargequantity, and a capacity changing portion capable of changing thecapacity of the floating diffusion in accordance with a capacitychanging signal, wherein the capacity of the floating diffusion ischanged by the capacity changing portion in a predetermined period inone readout period with respect to the accumulation period and aconversion gain is switched in the one readout period, and wherein thecapacity changing portion includes a MOS structure capacitor connectedto the floating diffusion, the MOS structure capacitor is changed ingate voltage by the capacity changing signal to change the capacity ofthe floating diffusion and switch the conversion gain of the floatingdiffusion; the solid-state imaging device further comprising a readoutportion for reading out a pixel signal from the pixel portion, whereineach pixel includes a reset element which discharges the charge of thefloating diffusion in a reset period, and the readout portion canperform, in one the readout period with respect to the accumulationperiod, a first conversion gain mode reading operation for reading out apixel signal by a first conversion gain in accordance with a firstcapacity which is set by the capacity changing portion and a secondconversion gain mode reading operation for reading out a pixel signal bya second conversion gain in accordance with a second capacity which isset by the capacity changing portion, performs a first operation of thefirst conversion gain mode reading operation in a first readout periodfollowing the reset period, then performs a first operation of thesecond conversion gain mode reading operation, performs transferprocessing for the transfer period by the transfer element after thefirst readout period in a state where the capacity of the floatingdiffusion is held at the second capacity corresponding to the secondconversion gain, and performs a second operation of the secondconversion gain mode reading operation in a second readout period afterthe transfer period, then performs a second operation of the firstconversion gain mode reading operation.